The lubrication properties of nanoconfined liquids underpin countless natural and industrial processes. However, our current understanding of lubricated friction is still limited, especially for nonideal interfaces exhibiting nanoscale chemical and topographical defects. Here, we use atomic force microscopy to explore the equilibrium and dynamical behavior of a model lubricant, squalane, confined between a diamond tip and graphite in the vicinity of an atomic step. We combine high-resolution imaging of the interface with highly localized shear measurements at different velocities and temperatures to derive a quantitative picture of the lubricated friction around surface defects. We show that defects tend to promote local molecular order and increase friction forces by reducing the number of stable molecular configurations in their immediate vicinity. The effect is general, can propagate over hundreds of nanometers, and can be quantitatively described by a semiempirical model that bridges the molecular details and mesoscale observations.

纳米受限液体的润滑特性支撑着无数自然和工业过程。但是，我们目前对润滑摩擦的理解仍然有限，尤其是对于表现出纳米级化学和形貌缺陷的非理想界面。在这里，我们使用原子力显微镜来研究模型润滑剂角鲨烷的平衡和动力学行为，该模型被限制在原子台阶附近的金刚石尖端和石墨之间。我们将界面的高分辨率成像与在不同速度和温度下的高度局部剪切测量相结合，以得出围绕表面缺陷的润滑摩擦的定量图像。我们显示缺陷倾向于通过减少在其附近的稳定分子构型的数量来促进局部分子有序并增加摩擦力。这种影响是普遍的，可以传播到数百纳米，并且可以通过桥接分子细节和中尺度观测的半经验模型进行定量描述。